A neuroanatomic study of the retinohypothalamic tract in the female albino rat

Joel David Levine, University of Pennsylvania


The retinohypothalamic tract (RHT) is a pathway that is necessary for the entrainment of circadian rhythms. Two sets of experiments which examine the RHT constitute this neuroanatomic study. The first set of experiments used cholera toxin conjugated to horseradish peroxidase, a sensitive neural tract tracer, to label the retinohypothalamic projections. Two components of the RHT were described. The medial component included projections into the preoptic area, suprachiasmatic nucleus, retrochiasmatic area, periventricular regions and the sub-paraventricular zone. The lateral component included light projections in the lateral hypothalamus and in the supraoptic nucleus (SON) and a well focused terminal field in the caudal peri-supraoptic nucleus region. Terminal label was also observed in the anterior dorsal and anterior ventral nuclei of the thalamus, bed nucleus of stria terminalis and the amygdala. The label in the supraoptic nucleus and peri-supraoptic nucleus region was surprising both because of the robust appearance of the peri-SON terminal field and the functional implication of a circuit mediating effects of light on posterior pituitary hormones. The second set of experiments employed a double labeling method following monocular injection of CT-HRP and pseudo rabies virus (PRV), a transsynaptic neuronal tracer, to identify retinorecipient neurons in the SON and peri-SON terminal field. Three strains of PRV were compared and strain differences were observed in the labeling of neurons in the peri-SON terminal field. In addition, pituitary injections of PRV retrogradely labeled cells in the peri-SON terminal field. These experiments demonstrate a direct projection from retina to neurons in the supraoptic nucleus and provides evidence for an indirect retino-SON projection via neurons in the peri-SON region. Implications for circadian and non-circadian photic effects are considered.

Subject Area

Anatomy & physiology|Neurology

Recommended Citation

Levine, Joel David, "A neuroanatomic study of the retinohypothalamic tract in the female albino rat" (1993). Dissertations available from ProQuest. AAI9321434.